The conventional method for defining patterns on wafers is photolithography technology. Patterns on reticles is projected on a substrate to expose photoresist material on the substrate. After the exposure of photoresist material, unexposed or exposed portions of the photoresist material is removed and a pattern, as same as the pattern on the reticles, is formed on the substrate. The photoresist layer with the patterns formed thereon usually serves as an etching mask in an etching process and the etching process forms patterns on thin film layer on the substrate.
Commonly, the linewidth limitation of integrated circuits is 20 determined by the ability of photolithography process. As the linewidth of integrated circuits is narrowed, the integrity of the integrated circuits is high. In addition, the shape of patterns formed on substrates is an important factor to decide whether or not the patterns are defined well. As usual, a photoresist pattern should be sharp enough so as to form a perfect pattern on a substrate that is under the photoresist pattern.
An approach to define a sharp photoresist pattern on a substrate involves the formation of a bottom anti-reflective coating (BARC) on a thin film layer and a pattern is then formed on the layer by using an etching process. During photolithography processes, BARC absorbs light that is projected toward wafers and reduces the reflective from the wafers in order to define sharp patterns on the wafers.
BARC material includes organic and inorganic material. Nevertheless, a sharp pattern is hardly formed on the thin film layer with organic BARC formed thereon. Commonly, silicon oxynitride material is indicated as inorganic BARC material and it is easily formed on substrates. But, a wet etching process is necessary for removing inorganic BARC from a substrate.
The organic bottom ARC is used for solving the reflective light causing the notching of photoresist. However, the organic BARC has the planarization effect and it is good for photolithography but not good for etching due to the various thickness of BARC. The oxynitride ARC film has solved the various thickness issue due to its conform film deposition. Again, the disadvantage of oxynitride ARC is not easy to remove after patterning.
Therefore, what is needed is a novel material for acting the BARC, which can be conformality formed on substrates and can be easily removed from substrates by using conventional dry etching process.
In SPIE vol. 1674 Optical/Laser Microlithography V, 1992, at pages 350-361, Yurika Suda et al. published a paper entitled of "A New Anti-reflective Layer for Deep UV lithography". In this paper, an anti-relfective layer (ARL) is used for in sub-half-micron and quarter-micron KrF excimer laser lithography and has the advantages including improved critical dimension (C.D.) contron with the resist thickness and reduction of notching caused by reflection from the substrate. An a-C:H ARL underneath the resist and then experimented to found the most suitable film conditions.Besides, the a-C:H ARL is organic and it can be ashed as same time as the resist. Also, since the exposure and focus latitudes are high, the new shceme is promising for single-layer resist processing with KrF excimer laser lithography.